Saturday, 5 August 2017

Change Register - Y Trechol - The Dominant Hills of Wales



Change Register

Y Trechol – The Dominant Hills of Wales


Y Trechol  – The Dominant Hills of Wales are the Welsh P30 hills whose prominence equal or exceed half that of their absolute height, with the minimum qualifying mark given as a percentage (50%).  The list was conceptualized after adding drop values to the hand written Master Lists that took in the P30 hills of Wales that were published on Geoff Crowder’s v-g.me website, this was during 2006 and 2007 and the compilation of what was to become Y Trechol – The Dominant Hills of Wales followed soon afterward.

The original title for the list was the UPP’s, an abbreviation for the Ultra Prominent Peaks of Wales; this title was later changed to The Dominant Hills of Wales.  The change of name was instigated after a discussion with Mark Trengove who informed me that the same concept of Dominance had been used by Eberhard Jurgalski in written format in 2001 and in published format in 2004.  I also realised that the original title could be confused with the listing of 5,000ft prominence world peaks that are known as the Ultras, their title having been shortened from the Ultra Prominent Peaks, as it was sensible not to use a working title that was similar to another that used different criteria I opted for the title of Y Trechol - The Dominant Hills of Wales, with the term of Dominance used to describe it, and the words Y Trechol being the Welsh for The Dominants.  Accompanying the main list is a sub list entitled The Lesser Dominant Hills of Wales, these are the additional P30 Welsh hills whose prominence is 33% or more and below 50% of their absolute height.

Although Y Trechol – The Dominant Hills of Wales was originally compiled in 2006 – 2007 after drop values were added to the Welsh P30 lists, the listing did not commence publication until 3rd December 2015, with ‘commence’ being the operative word as this is ongoing with bi-weekly, monthly, bi-monthly or quarterly instalments of hill groups being published on Mapping Mountains.

Although the criteria has remained the same in the Dominant and Lesser Dominant list, the listing has benefited greatly since its first compilation with the advent of independent surveyors using GPS / GNSS receivers,  the analysis of LIDAR data and the availability of an expanded range of online Ordnance Survey maps all adding greater accuracy to the numerical data.  However, it is not just numerical data that has seen this list develop since its first inception, as local enquiry and historical research are enhancing the place-name data used for the listed hill names.

It seems fitting that the list of Y Trechol – The Dominant Hills of Wales should now benefit from a detailed Change Register, and although the changes to this list have been catalogued on the Mapping Mountains site it will be useful to list all status changes to the list since first compilation and present them in a Change Register.

The Change Register to Y Trechol – The Dominant Hills of Wales appears below with the reclassifications to the Dominant list being detailed chronologically in receding order.



Change Register

Y Trechol – The Dominant Hills of Wales






Carn Ysgubor    102.4m at SM 69953 24603 

Carn Ysgubor (SM 699 246) has now been reclassified back into the ranks of Lesser Dominant hills

This hill was originally listed as a Lesser Dominant and subsequently reclassified to a Dominant hill based on the result of a survey conducted with the Trimble GeoXH 6000 (see below), the adoption of OSGM15 has resulted in accurately known heights in Wales increasing by approximately 2-4cm and this has resulted in Carn Ysgubor being reclassified back to Lesser Dominant status.  The announcement of this hill’s reclassification back to a Lesser Dominant hill was made on the Mapping Mountains site on 05.07.17, the hill was previously listed with 50.00% Dominance based on the 102.4m summit and 51.2m bwlch heights produced by a survey with the Trimble GeoXH 6000 conducted by Myrddyn Phillips on the 15.05.16, these values when converted to OSGM15 are 102.395m summit and 51.208m bwlch heights, with these values giving 51.187m drop and 49.99% Dominance.  Dominant total decreases by one and confirmed as 258.





Carn Ysgubor    102.4m at SM 69953 24603 

Prior to OSGM15 conversion the Trimble GeoXH 6000 survey of Carn Ysgubor (SM 699 246) reclassified it from a Lesser Dominant to a Dominant hill

The announcement of this hill’s reclassification from a Lesser Dominant to a Dominant hill was made on the Mapping Mountains site on 09.06.16 with the Hill Reclassifications post being published on the 10.06.16, the hill was previously listed with 49.50% Dominance based on the 101m summit spot height on the Ordnance Survey 1:25,000 Explorer map and an estimated bwlch height of c 51m based on interpolation of  bwlch contouring between 50m – 55m, with these values giving this hill c 50m of drop.  This hill was subsequently surveyed with the Trimble GeoXH 6000 by Myrddyn Phillips on 15.05.16, resulting in the summit height being 102.4m and the bwlch height being 51.2m, giving a drop value of 51.2m and a Dominance value of 50.00%.  The survey data for this hill has subsequently been converted to OSGM15 resulting in the hill being reclassified back to Lesser Dominant status (see above).  Dominant total increases by one and confirmed as 259.





Pt. 119m    119m at SH 72136 00406 

The details relating to this hill were re-evaluated and completed on the 06.06.16 resulting in it being reclassified from a Lesser Dominant hill to a Dominant hill, with this being announced on Mapping Mountains on the 03.12.16 when the Tarennydd group of hills were published, with a retrospective Hill Reclassifications post appearing on Mapping Mountains on 28.05.17.  The hill was previously listed with 48.25% Dominance based on an estimated c 114m summit height and a 59m bwlch height which appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps, and its reclassification is due to the 119m summit spot height that appears on the Ordnance Survey enlarged mapping hosted on the Geograph website which is sufficient for this hill to qualify as a Dominant hill.  Dominant total increases by one and confirmed as 258.





Ynys Fach    30.8m at SM 82209 32743 

Ynys Fach (SM 822 327) a marvelous hill whatever its Dominance

The deletion of this hill from Dominant status was announced on Mapping Mountains on the 06.06.16, with the survey that resulted in this hill’s deletion being conducted on the 14.05.16, and the Hill Reclassifications post being published on Mapping Mountains on the 08.06.16, the hill was previously listed with 100.00% Dominance based on an estimated c 31m summit height and the same drop value.  The hill has subsequently been surveyed using a Trimble GeoXH 6000 by Myrddyn Phillips, resulting in a 30.8m (converted to OSGM15) summit height and a 1.2m (converted to OSGM15) bwlch height, with these values giving this hill 29.6m of drop, which is insufficient for it to be considered for Dominant status.  Dominant total decreases by one and confirmed as 257.





Moelfre    74.1m at SH 55830 37553 

Moelfre (SH 558 375) is now reclassified from a Dominant to a Lesser Dominant hill

The announcement of this hill’s reclassification from a Dominant to a Lesser Dominant was made on the Mapping Mountains site on 03.03.16 with the Hill Reclassifications post being published on the 04.03.16, the hill was previously listed with 50.00% Dominance based on the 74m summit spot height on the Ordnance Survey enlarged mapping hosted on the Geograph website and an estimated bwlch height of c 37m based on bwlch contouring between 35m – 40m.  This hill was subsequently surveyed with the Trimble GeoXH 6000 by Myrddyn Phillips on 23.02.16, resulting in the summit height being 74.1m (converted to OSGM15) and the bwlch height being 37.8m (converted to OSGM15), giving a drop value of 36.3m and a Dominance of only 49.00%, which is insufficient for it to retain its Dominant status.  Dominant total decreases by one and confirmed as 258.





Pt. 66m    66m at SH 29957 27041 

This hill’s reclassification to a Dominant hill was announced on the 11.02.16 when the Pen Llŷn group of hills was published on Mapping Mountains, with a retrospective Hill Reclassifications post appearing on Mapping Mountains on 19.03.17, the hill was previously listed with 48.44% Dominance based on a 64m map heighted summit at SH 295 266.  In recent times the Ordnance Survey larger scaled mapping has become available on the Geograph website and this more detailed map shows a 66m summit spot height at SH 299 270 and a connecting 32m bwlch spot height, with the subsequent drop of 34m sufficient for this hill to qualify as a Dominant hill with 51.52% Dominance.  Dominant total increases by one and confirmed as 259.





Bodlondeb Wood    c 57m at SH 77923 78114 

The inclusion of this hill in the listing of Y Trechol – The Dominant Hills of Wales was on the 17.12 15 via the publication on Mapping Mountains of the hill grouping it is a part of, with a retrospective Hill Reclassifications post appearing on the 18.02.17.  The hill had previously been unclassified due to lack of detail on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps giving only a 50m uppermost ring contour and bwlch contouring between 20m – 30m,  however with the advent of 5m contour intervals on the Ordnance Survey enlarged mapping hosted on the Geograph website a more detailed estimation of its drop value and therefore its Dominance could be given, and with a drop value of c 34m based on an estimated summit height of c 57m and an estimated bwlch height of c 23m, the hill is now listed with a Dominance of 59.65%.  Dominant total increases by one and confirmed as 258. 




3rd December 2015 – Mapping Mountains starts publication of Y Trechol The Dominant Hills of Wales. 

Dominant total confirmed as 257.





Bryn Mawr    178.1m at SJ 25117 19054 

The wooded summit of Bryn Mawr (SJ 251 190)

The reclassification of this hill from a Lesser Dominant to a Dominant hill was due to a survey conducted by Myrddyn Phillips with the Trimble GeoXH 6000 on the 08.08.15, with its details appearing in the Carnedd Wen group of hills when published on Mapping Mountains on the 03.06.17, with a retrospective Hill Reclassifications post appearing on Mapping Mountains on 16.07.17, the hill was previously listed with 49.13% Dominance based on an estimated c 173m summit height and an estimated c 88m bwlch height, with the latter height later confirmed via an 88m spot height appearing on the Ordnance Survey enlarged mapping hosted on the Geograph website.  The subsequent survey with the Trimble produced a 178.1m (converted to OSGM15) summit height, giving this hill 90m of drop and 50.53% Dominance.  Dominant total increases by one and confirmed as 257.





Carreglefain    260.7m at SH 32421 41054 

Carreglefain (SH 324 410) is now listed as a Dominant hill after a survey with the Trimble GeoXH 6000

The announcement of this hill’s reclassification from a Lesser Dominant to a Dominant hill was made on the Mapping Mountains site on 01.12.14 with the Hill Reclassifications post being published on the 20.03.17, the hill was previously listed with 48.66% Dominance based on the 261m summit spot height on the Ordnance Survey 1:25,000 Explorer map and an estimated bwlch height of c 134m based on bwlch contouring between 130m – 140m.  This hill was subsequently surveyed with the Trimble GeoXH 6000 by Myrddyn Phillips on 24.11.14, resulting in the summit height being 260.7m (converted to OSGM15) and the bwlch height being 130.1m (converted to OSGM15), giving a drop value of 130.6m and a Dominance value of 50.08%.  Dominant total increases by one and confirmed as 256.





Castell Cricieth    49.6m at SH 50003 37733 

Castell Cricieth (SH 500 377) was accepted as a Dominant hill after its introduction into the P30 ranks

This hill was included as a Dominant hill shortly after Alex Cameron first proposed its inclusion as a new P30 in September 2014, with the hill appearing in its respective hill grouping of Moel Hebog when published on Mapping Mountains on 28.01.16 and a retrospective Hill Reclassifications post appearing on Mapping Mountains on 07.03.17.  The hill had previously been unclassified as with an uppermost 30m ring contour on Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps and bwlch contouring between 10m – 20m it was deemed not to have the minimum 3om of drop required for consideration as a Dominant hill.  However, the Ordnance Survey enlarged mapping hosted on the Geograph website has contour intervals at 5m and with a 48m summit spot height and an estimated bwlch height of c 18m, these values gave this hill c 30m of drop and 62.50% of Dominance.  The hill has subsequently been surveyed with the Trimble GeoXH 6000 by Myrddyn Phillips on the 15.06.15 with the details relating to this survey being published on Mapping Mountains on the 27.06.15, resulting in a 49.6m (converted to OSGM15) summit height and a 19.3m (converted to OSGM15) bwlch height, giving 30.3m drop and 61.02% Dominance.  Dominant total increases by one and confirmed as 255.





Pt. 68.2m    68.2m at SH 38337 94993 

Pt. 68.2m (SH 383 949) is now listed as a Lesser Dominant hill

The reclassification of this hill to a Lesser Dominant was announced on the Mapping Mountains site on 13.09.14 with the Hill Reclassifications post appearing on the 07.12.15, the hill was previously listed with 50.75% Dominance based on the 67m spot height that appears on the Ordnance Survey enlarged mapping hosted on the Geograph website and an estimated bwlch height of c 33m, with these values giving this hill c 34m of drop.  This hill was subsequently surveyed with the Trimble GeoXH 6000 by Myrddyn Phillips and Alex Cameron on 07.09.14, resulting in the summit height being 68.2m (converted to OSGM15) and the bwlch height being 34.2m (converted to OSGM15), giving a drop value of 34.0m and a Dominance of only 49.85%, which is insufficient for it to retain its Dominant status.  Dominant total decreases by one and confirmed as 254.





Ynys Glog    40.6m at SH 59647 39826 

Ynys Glog (SH 596 398) is now listed as a Dominant hill

The inclusion of this hill in the Dominant list took place shortly after Aled Williams first proposed it as a new P30 in early 2014, with a Hill Reclassifications post detailing its new status as a P30 appearing on the Mapping Mountains site on 05.02.14, the hill was subsequently listed in the Moelwynion group of Dominant hills when published on Mapping Mountains on 25.02.16, with a retrospective Hill Reclassifications post for its status as a Dominant hill appearing on the 07.04.17.  Prior to this hill being listed as a P30 it had not been classified as contouring on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps implied that it did not have the required minimum 30m of drop to be included as a P30 and therefore be considered for Dominant status.  With the advent of on-line mapping and especially the Ordnance Survey enlarged mapping hosted on the Geograph website there is now greater opportunity to analyse numerical data and with a 42m summit spot height and an estimated c 8m bwlch height on this enlarged map it gave this hill c 34m of drop and 80.95% Dominance.  The hill has subsequently been surveyed using a Trimble GeoXH 6000 by Myrddyn Phillips and Aled Williams on the 21.11.14 resulting in a 40.6m (converted to OSGM15) summit height and a 7.9m (converted to OSGM15) bwlch height, giving 32.7m of drop and 80.44% Dominance.  Dominant total increases by one and confirmed as 255.





Ynys Berfedd    42.9m at SH 59943 39865 

The wooded and rocky slopes of Ynys Berfedd (SH 599 398)

This hill was included in the Dominant list shortly after Aled Williams first proposed its inclusion as a new P30 in early 2014, with a Hill Reclassifications post detailing its new P30 status appearing on Mapping Mountains on 05.02.14, the hill then appeared in the Moelwynion group of Dominant hills when published on Mapping Mountains on 25.02.16, with a retrospective Hill Reclassifications post for its status as a Dominant hill appearing on the 06.04.17.  The hill had previously appeared in the sub list that accompanied the original Welsh P30 lists when published on Geoff Crowder’s v-g.me website, with map contouring on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer maps implying that it did not have the required minimum 30m of drop to be included in the main list.  However, the Ordnance Survey enlarged mapping hosted on the Geograph website has a 43m summit spot height, and with an estimated c 6m bwlch height this gave the hill c 37m of drop and sufficient Dominance to be included in Y Trechol – The Dominant Hills of Wales.  The hill has subsequently been surveyed using a Trimble GeoXH 6000 by Myrddyn Phillips and Aled Williams on the 21.11.14 resulting in a 42.9m (converted to OSGM15) summit height and a 6.8m (converted to OSGM15) bwlch height, giving 36.1m of drop and 84.06% Dominance.  Dominant total increases by one and confirmed as 254.





Ynys Hir    37.3m at SH 56695 39693 

The wooded surrounds of Ynys Hir (SH 566 396)

This hill’s inclusion as a new P30 and Dominant hill was announced on Mapping Mountains on 02.02.14 with the Hill Reclassifications post being published on the 26.02.17, the hill was previously unclassified as detail on a variety of different scaled Ordnance Survey maps implied that it did not have the minimum 30m of drop required to be considered for Dominant status.  This hill was subsequently surveyed with the Trimble GeoXH 6000 by Myrddyn Phillips and Aled Williams on the 01.02.14, and it was Aled who suggested visiting the hill and its potential as a new P30, resulting in a survey height of 37.3m (converted to OSGM15) for the summit and with an estimated bwlch height of c 3m, these values give this hill c 34m of drop and 91.21% of Dominance.  Dominant total increases by one and confirmed as 253.




31st November 2012 – Compilation of hand written list completed of Y Trechol The Dominant Hills of Wales.

Dominant total confirmed as 252.





Carreg Rhoson    c 30m at SM 67235 25678 

The islets making up Carreg Rhoson (SM 672 256) with the highest island now listed as a Dominant hill

This hill was the second of two added to the Dominant list shortly after its initial compilation was completed with the date of 31.10.12 recorded against the two additions, prior to this it was unclassified and did not appear in the P30 list on Geoff Crowder’s v-g.me website as its uppermost 30m ring contour on the Ordnance Survey 1:25,000 Explorer map had not been spotted, the advent of the enlarged mapping hosted on the Geograph website with its greater scale and definition meant that the small 30m ring contour was easier to see and therefore this hill, which is an island, qualifies for P30 status as well as Dominant status, with a retrospective Hill Reclassifications post appearing on the Mapping Mountains site on 09.03.17.  Dominant total increases by one and confirmed as 252.





Dinas Dinlle    34.7m at SH 43676 56438 

Dinas Dinlle (SH 436 564) is now listed in the ranks of Dominant hills

This hill was one of two added to the Dominant list shortly after its initial compilation with the date of 31.10.12 recorded against the two additions, prior to this its potential inclusion as a P30 was first spotted by Chris Watson, with the hill appearing in its respective hill grouping when published on Mapping Mountains on 28.01.16 and a retrospective Hill Reclassifications post appearing on Mapping Mountains on 24.02.17.  The hill had previously been unclassified with a 31m summit spot height on the Ordnance Survey 1:50,000 Landranger and bwlch contouring between 0m – 10m on this and the 1:25,000 Explorer map, these details implied that the hill did not have 30m of drop which is the minimum required for consideration to Dominant status.  However, the Ordnance Survey enlarged mapping hosted on the Geograph website has contour intervals at 5m and with an uppermost ring contour of 35m and bwlch contouring between 0m – 5m it meant that this hill had sufficient prominence and Dominance to be included in this list.  The hill’s summit was subsequently surveyed with the Trimble GeoXH 6000 by Myrddyn Phillips and Bryn Phillips on the 26.12.13 with the details relating to this survey being published on Mapping Mountains on the 03.01.14, with the 34.7m (converted to OSGM15) summit height and c 3m bwlch height sufficient for this hill’s inclusion as a Dominant hill with 92.16% Dominance.  Dominant total increases by one and confirmed as 251.





Ynys Gron    69.4m at SH 59653 39268 

The Trimble GeoXH 6000 gathering data at the highest point of what remains of Ynys Gron (SH 596 392)

This hill was deleted from the Dominant list after 22.03.12 and was retrospectively reported on Mapping Mountains with a Hill Reclassifications post on the 05.04.17, with the hill having been excluded from the Moelwynion group of hills when these were published on Mapping Mountains on the 25.02.16.  The hill had previously been classified with 52.08% Dominance based on the Ordnance Survey 96m summit spot height on the 1:25,000 Outdoor Leisure map and an estimated drop of c 50m, this was reassessed when more up-to-date on-line mapping became available that showed this hill’s summit to have been quarried.  The hill has subsequently been surveyed using a Trimble GeoXH 6000 by Myrddyn Phillips on the 25.11.14, resulting in a 69.4m (converted to OSGM15) summit height and a 44.3m (converted to OSGM15) bwlch height, with these values giving this hill 25.1m of drop, which is insufficient for it to be considered for Dominant status.  Dominant total decreases by one and confirmed as 250.





Geirth Mawr    56m at SH 53512 39361 

The deletion of this hill from the listing of Y Trechol – The Dominant Hills of Wales took place after 22.03.12 and was retrospectively reported on Mapping Mountains with a Hill Reclassifications post on the 21.02.17, with the hill having been excluded from the Moel Hebog group of hills when these were published on Mapping Mountains on the 28.01.16.  The hill had previously been classified with 51.72% Dominance based on a c 58m summit height and a 28m bwlch height, this was rectified when the Ordnance Survey enlarged mapping on the Geograph website was examined prior to publication on Mapping Mountains, and as this scale of mapping has a 56m summit spot height it gives this hill only 28m of drop, which is insufficient for Dominant inclusion.  Dominant total decreases by one and confirmed as 251.




11th April 2011 – Started compilation of hand written list of Y Trechol The Dominant Hills of Wales.

Dominant total confirmed as 252.




23rd April 2009 – Criteria established and first hill purposely bagged that met the criteria of Y Trechol The Dominant Hills of Wales.

Dominant total confirmed as 252.









Myrddyn Phillips (August 2017)

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